1 - Well I am assuming that the ore was in a creek when I found it, and the cadmium / mercury and other toxins were in the ore in the creek and so already in the pipeline to the drinking water. So by removing, and then moving them to higher ground, am i not simply relocating the toxins further away from the drinking waters ? Or, are these toxins in a state of perpetual prison in the ore, locked away, never to be released into the water naturally ? Since you have no assay we really do not know if they are there. But by roasting it it oxidizes and volatilizes into a state wher it may be taken up by organic beeings. Even more if it is dissolved by acids and such converted to an ionic salt.
2 - Charcoal also contains coal dust and mercury and cadmium and arsenic... Enjoy your steak ; ) I was just pointing out that Charcoal ash is often simply dumped into a garden or in the yard by millions of people. Never mind the other millions who stand in the smoke over the grill breathing it, along with the CO.... Oh, and they live ! Sometimes to ripe old ages. (no diminishing of threat, again, just trying to put it into perspective).
Scale it out for me if you can, on a scale of 1 to 10, with 10 being the most hazardous.
1 - Is Charcoal and the human activity around it (ie. - no mask, standing in the smoke, and dumping in the yard and garden) a 5 ...
2 - Is the human activity around AR ore assay process (ie. - avoiding smoke, dumping in Ash , burning, and relocating to high ground) a 10 ..
.... or is it about a push.. both just not so good for you, or those around you.... but everyone will probably still live if they don't eat too many hot dogs. Charcoal has its own challenges, many metals amongst them Gold will reduce to metallic stat in contact with Carbon and when burnt will become volatile and go into the air. CO is not accumulative , the danger from CO comes from the fact that it has greater affinity to our blood than Oxygen alone, but it will leave the body relatively fast, these other substances will not, Mercury and Cadmium will stay in the body practically until the end. There may be drugs that scavenge it, I really do not know. The relative dangers of these has with dosage as everything else, the scary part of Hg and Cd is that it is cumulative so the daily doses should be as small as possible.